For many years, the design of concrete structures imitated typical steel design of column, girder and beam. With technological advances in structural concrete, however, its own form began to evolve. Concrete has the advantages of lower cost than steel, of not requiring fireproofing, and of its plasticity, a quality that lends itself to free flowing or boldly massive architectural concepts. On the other hand, structural concrete, though quite capable of carrying almost any compressive (vertical) load, is extremely weak in carrying significant tensile loads. It becomes necessary, therefore, to add steel bars, called reinforcements, to concrete, thus allowing the concrete to carry the compressive forces and the steel to carry the tensile (horizontal) forces.
Structures of reinforced concrete may be constructed with load-bearing walls, but this method does not use the full potentialities of the concrete. The skeleton frame, in which the floors and roofs rest directly on exterior and interior reinforced-concrete columns, has proven to be most economic and popular. Reinforced concrete framing is seemingly a quite simple form of construction. First, wood or steel forms are constructed in the sizes, positions, and shapes called for by engineering and design requirements. The steel reinforcing is then placed and held in position by wires at its intersections. Devices known as chairs and spacers are used to keep the reinforcing bars apart and raised off the form work. The size an number of the steel bars depends completely upon the imposed loads and the need to transfer these loads evenly throughout the building and down to the foundation. After the reinforcing is set in place, the concrete, a mixture of water, cement, sand, and stone or aggregate, of proportions calculated to produce the required strength, is placed, care being taken to prevent voids or honeycombs.
One of the simplest designs in concrete frames is the beam-and-slab. This system follows ordinary steel design that uses concrete beams that are cast integrally with the floor slabs. The beam-and-slab system is often used in apartment buildings and other structures where the beams are not visually objectionable and can be hidden. The reinforcement is simple and the forms for casting can be utilized over and over for the same shape. The system, therefore, produces an economically viable structure. With the development of flat-slab construction, exposed beams can be eliminated. In this system, reinforcing bars are projected at right angles and in two directions from every column supporting flat slabs spanning twelve or fifteen feet in both directions.
Reinforced concrete reaches its highest potentialities when it is used in pre-stressed or post-tensioned members. Spans as great as 100 feet can be attained in members as deep as three feet for roof loads. The basic principal is simple. In pre-stressing, reinforcing rods of high tensile strength wires are stretched to a certain determined limit and then high-strength concrete is placed around them. When the concrete has set, it holds the steel in a tight grip, preventing slippage or sagging. Post-tensioning follows the same principal, but the reinforcing is held loosely in place while the concrete is placed around it. The reinforcing is then stretched by hydraulic jacks and securely anchored into place. Pre-stressing is done with individual members in the shop and post-tensioning as part of the structure on the site.
In a typical tendon tensioning anchor assembly in such post-tensioning operations, there is provided a pair of anchors for anchoring the ends of the tendons suspended therebetween. In the course of installing the tendon tensioning anchor assembly in a concrete structure, a hydraulic jack or the like is releasably attached to one of the exposed ends of the tendon for applying a predetermined amount of tension to the tendon. When the desired amount of tension is applied to the tendon, wedges, threaded nuts, or the like, are used to capture the tendon and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition.
In such post-tension construction, the tendons are anchored and cut off just inside the face of the structure in what are termed "pockets". The "pockets" surrounding the tendon end are filled with a concrete grout. A "pocketformer" is placed in the concrete adjacent to the face of the structure and against an end of the terminal anchor. After the concrete is suitably hardened, a form board is removed and the pocketformer is removed so as to expose the pocket. The ends of the tendon extend outwardly of the pocket. After the tensioning has occurred, the pocket is then filled with a concrete grout so as to be flush with the face of the structure.
FIG. 1 shows a pocketformer 10 as used in the prior art. This pocketformer 10 has a frustoconical surface 12 formed on the exterior of the pocketformer 10. The frustoconical shape 12 will define the pocket. A central tubular member 14 is formed within the interior of the frustoconical portion 12. One end 18 of the tubular member 14 will extend into the central bore of the anchor. The interior 16 of the tubular member 14 will allow the tendon to extend therethrough. Struts 20 extend between the tubular member 14 and the frustoconical portion 12. The tubular member 14 is generally centered within the interior of the frustoconical portion 12. The surface of the anchor will abut the narrow end of the frustoconical portion 12. The wide end of the frustoconical portion will abut a surface of a form board. The tubular member 14 extends through a hole formed in the form board. As such, the tendon will extend outwardly of the form board during the formation of the concrete structure.
One of the problems with the pocketformer 10, as shown in FIG. 1, is the inability to properly secure the anchor relative to the pocketformer 10. In conventional practice, long threaded members will extend through holes in the anchor member and be attached to the form board. After the concrete is hardened, it will be necessary to remove the threaded members or nails. If these items are not removed, then corrosion can occur and rust patterns will form on the facing surface of the concrete structure. Furthermore, the use of nails or threaded members for securing the anchor relative to the form board is a time consuming and labor-intensive operation. As such, a need has developed so as to allow the anchor to be removably secured to the pocketformer during the installation of the pocketformer.
In the past, various patents have issued relating to pocketformers that serve to retain the pocketformer in place, against the form board, during the installation of the anchor. For example, U.S. Pat. No. 3,844,697, issued on Oct. 29, 1974 to H. J. W. Edwards describes an anchorage assembly including an anchor having a hollow housing and a means therein for engaging a stressing tendon passing therethrough. The hollow member is removably attached to the anchor housing and to the concrete formwork and fixing the relative position of the anchor housing to the formwork. The member surrounds the tendon between the anchor housing and the formwork and is adapted and arranged to be detached from the anchor housing after the concrete has set. A cavity forming spacer is provided which surrounds the member and is disposed between and seals against the anchor housing and the formwork to form a cavity in the concrete.
U.S. Pat. No. 3,956,797, issued on May 18, 1976 to Brandestini describes a pocketformer apparatus in which the pocketformer is initially threaded into the interior opening of a steel anchor. As such, the steel anchor will have internal threads which threadedly receive the external threads on the end of the pocketformer. The pocketformer includes an interior bore through which the tendon passes. On the opposite end of the pocketformer is a threaded section which extends on an opposite side of the form board from the anchor. A threaded nut is threadedly received by the threads of the pocketformer which extend on the opposite side of the form board.
U.S. Pat. No. 4,053,974, issued on Oct. 18, 1977 to Howlett et al. describes a method of forming a concrete structure with a recess to receive an anchorage. This method includes a tubular mounting means mounted to extend over the tendon and through an opening in a bearing or anchor plate in order to secure the bearing plate in a fixed position aligned in relation to the tendon for casting the bearing plate into the concrete member in a predetermined orientation. A spacing means is provided between the form board and the anchor plate so as to allow the anchor plate to be cast into a recess in the concrete member.
U.S. Pat. No. 4,363,462, issued on Dec. 14, 1982 to Wldodkowski et al. teaches a formwork for a concrete structural member. This device includes a recoverable formwork part. The recoverable part has an axially elongated sheath which closely encloses a tendon. A cup-shaped part is formed integrally with the sheath and is arranged to form at least a portion of the recess in the concrete member. When assembled on the formwork, one end of the sheath is arranged to be located within the concrete when it is poured and the other end is located on the exterior of the formwork. The cup-shaped part is located intermediate of the ends of the sheath and just inside the formwork. A member is engagable with the sheath for attaching it to the formwork.
It is an object of the present invention to provide a pocketformer which allows the anchor to be properly secured in place relative to the form board.
It is another object of the present invention to provide a pocketformer that allows the pocketformer to be removably attached by snap-fitting to the anchor.
It is a further object of the present invention to provide a pocketformer which is adaptable to conventional anchors.
It is still another object of the present invention to provide a pocketformer which eliminates the need for nails or threaded members for the attachment of the anchor relative to the form board.
It is still another object of the present invention to provide a pocketformer apparatus which is easy to use, relatively inexpensive, and easy to manufacture.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.